kernel: use accepted version of bcm47xxpart fix commit

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

1 files changed, 70 insertions, 0 deletions

diff --git a/target/linux/generic/backport-4.9/069-v4.18-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch b/target/linux/generic/backport-4.9/069-v4.18-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch
new file mode 100644
index 0000000000..e08f8dad32
--- /dev/null
+++ b/target/linux/generic/backport-4.9/069-v4.18-mtd-bcm47xxpart-improve-handling-TRX-partition-size.patch
@@ -0,0 +1,70 @@
+From 237ea0d4762cc14d0fc80e80d61f0f08e1050c7f Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
+Date: Thu, 12 Apr 2018 07:24:52 +0200
+Subject: [PATCH] mtd: bcm47xxpart: improve handling TRX partition size
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+When bcm47xxpart finds a TRX partition (container) it's supposed to jump
+to the end of it and keep looking for more partitions. TRX and its
+subpartitions are handled by a separate parser.
+
+The problem with old code was relying on the length specified in a TRX
+header. That isn't reliable as TRX is commonly modified to have checksum
+cover only non-changing subpartitions. Otherwise modifying e.g. a rootfs
+would result in CRC32 mismatch and bootloader refusing to boot a
+firmware.
+
+Fix it by trying better to figure out a real TRX size. We can securely
+assume that TRX has to cover all subpartitions and the last one is at
+least of a block size in size. Then compare it with a length field.
+
+This makes code more optimal & reliable thanks to skipping data that
+shouldn't be parsed.
+
+Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
+Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
+---
+ drivers/mtd/bcm47xxpart.c | 22 ++++++++++++++++++----
+ 1 file changed, 18 insertions(+), 4 deletions(-)
+
+--- a/drivers/mtd/bcm47xxpart.c
++++ b/drivers/mtd/bcm47xxpart.c
+@@ -186,6 +186,8 @@ static int bcm47xxpart_parse(struct mtd_
+ 		/* TRX */
+ 		if (buf[0x000 / 4] == TRX_MAGIC) {
+ 			struct trx_header *trx;
++			uint32_t last_subpart;
++			uint32_t trx_size;
+ 
+ 			if (trx_num >= ARRAY_SIZE(trx_parts))
+ 				pr_warn("No enough space to store another TRX found at 0x%X\n",
+@@ -195,11 +197,23 @@ static int bcm47xxpart_parse(struct mtd_
+ 			bcm47xxpart_add_part(&parts[curr_part++], "firmware",
+ 					     offset, 0);
+ 
+-			/* Jump to the end of TRX */
++			/*
++			 * Try to find TRX size. The "length" field isn't fully
++			 * reliable as it could be decreased to make CRC32 cover
++			 * only part of TRX data. It's commonly used as checksum
++			 * can't cover e.g. ever-changing rootfs partition.
++			 * Use offsets as helpers for assuming min TRX size.
++			 */
+ 			trx = (struct trx_header *)buf;
+-			offset = roundup(offset + trx->length, blocksize);
+-			/* Next loop iteration will increase the offset */
+-			offset -= blocksize;
++			last_subpart = max3(trx->offset[0], trx->offset[1],
++					    trx->offset[2]);
++			trx_size = max(trx->length, last_subpart + blocksize);
++
++			/*
++			 * Skip the TRX data. Decrease offset by block size as
++			 * the next loop iteration will increase it.
++			 */
++			offset += roundup(trx_size, blocksize) - blocksize;
+ 			continue;
+ 		}
+